Electronic cigarettes (EC) are battery powered nicotine delivery devices that aerosolize nicotine. Despite the increasing use of EC, little attention has been paid to their possible adverse effects on human health. Theoretically, the risk relates to nicotine per se and/or the propellants or contaminants in the EC aerosol. The hypothesis underlying our application is that chronic EC smoking disorders the biology of the oral epithelium, the first cell population exposed to inhaled EC vapors. There is compelling evidence to support this hypothesis: (1) EC vapors contain nicotine, the oral epithelium expresses nicotine receptors, and exposure of epithelia to nicotine activates the nicotine pathway; (2) EC vapors also contain contaminants that potentially can affect oral epithelial biology; and (3) in vitro studies suggest that EC vapors modify epithelial biology and data generated by our laboratory demonstrates that even a brief, acute exposure of healthy nonsmokers to EC vapors induces significant changes in the airway epithelial transcriptome, including the expression of genes in the nicotine and p53 pathways. Using a cross-sectional, cohort-comparison of EC smokers compared to age, gender and ethnicity-matched never smokers, we propose to assess the oral epithelium obtained by biopsy from 200 EC smokers and 50 nonsmokers. The EC study cohort will be restricted to young adults (age 21-35 yr) with no prior history of tobacco smoking, but who have smoked EC for >6 months. With the knowledge that disordering of cell biology occurs long before clinical disease, we will evaluate the oral epithelium at the epigenome (DNA methylation) and transcriptome (mRNA and miRNA) levels (Specific Aim 1). With the complementary expertise of the co-PIs (R. Crystal, biology of the epithelium, J. Mezey, computational biology), by integrating analysis at the epigenome and transcriptome levels, we will identify gene(s)/pathways/communities disordered by EC vapors (Specific Aim 2). Based on our preliminary data, we will initially focus on the nicotine, p53 and related pathways at the protein and post-translational levels. Because there is so little known about the effects of EC smoking on the oral epithelium, we cannot predict which other biologic processes will be affected, but it is likely that EC vapors influence biology linked to host defens and/or early carcinogenesis. Based on these considerations, we propose 2 Specific Aims. Specific Aim 1: To evaluate the hypothesis that EC smoking alters oral epithelial biology, biopsies will be collected from the buccal mucosa of chronic EC smokers and healthy nonsmoker controls, none of whom have a history of smoking any tobacco products. Genome-wide datasets will be generated to assess DNA methylation and both coding and non-coding RNA transcriptomes. Specific Aim 2: Using both computational and experimental approaches, the biopsies and genome-wide datasets generated in Specific Aim 1 will be assessed to identify genes, pathways and gene communities altered in the oral epithelium of EC smokers, including analyses of two pathways (nicotine, p53) identified in our pilot study.